The circuit uses four PL519 Television line output valves inside a very simple circuit that will deliver above 450 watts at 3.5 MHz (350 watts at 30 MHz). PL519 (40KG6A) is a far more robust substitute for the earlier PL509 (40KG6) tube. Each valves will do the job properly in this circuit. The input drive power is about 50 - 100 watts so it really is working with most amateur radio HF transmitters. Not shown in the circuit will be the cooling fan that is needed to force air across the valves to cool them. In operation the 1K0 pot is adjusted to set the complete valve anode electric current to close to 50mA to 70 mA.
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